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FreeBSD-EN-18:11.listen                                         Errata Notice
                                                          The FreeBSD Project

Topic:          Denial of service in listen syscall over IPv6 socket

Category:       core
Module:         kernel
Announced:      2018-09-27
Credits:        Jakub Jirasek, Secunia Research at Flexera
Affects:        All supported versions of FreeBSD.
Corrected:      2018-09-27 18:50:10 UTC (stable/11, 11.2-STABLE)
                2018-09-27 18:34:42 UTC (releng/11.2, 11.2-RELEASE-p4)
                2018-09-27 18:34:42 UTC (releng/11.1, 11.1-RELEASE-p15)
                2018-09-27 18:48:50 UTC (stable/10, 10.4-STABLE)
                2018-09-27 18:34:42 UTC (releng/10.4, 10.4-RELEASE-p13)
CVE Name:       CVE-2018-6925

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

The protocol control block is a structure that maintains the network layer
state for various sockets.  There are various state flags that must be
properly maintained to keep the structure consistent.

II.  Problem Description

There are various cases in the IPv6 socket code where the protocol control
block's state flags are modified during a syscall, but are not restored if
the operation fails.  This can leave the control block in an inconsistent
state.

III. Impact

A local unprivileged user could exploit the inconsistent state of the
protocol control block to cause the kernel to crash, leading to a denial of
service.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

Afterward, reboot the system.

2) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Afterward, reboot the system.

3) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 11.x]
# fetch https://security.FreeBSD.org/patches/EN-18:11/listen-11.patch
# fetch https://security.FreeBSD.org/patches/EN-18:11/listen-11.patch.asc
# gpg --verify listen-11.patch.asc

[FreeBSD 10.4]
# fetch https://security.FreeBSD.org/patches/EN-18:11/listen-10.patch
# fetch https://security.FreeBSD.org/patches/EN-18:11/listen-10.patch.asc
# gpg --verify listen-10.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r338985
releng/10.4/                                                      r338980
stable/11/                                                        r338986
releng/11.1/                                                      r338980
releng/11.2/                                                      r338980
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-6925>

For information about Secunia Research:
<URL:https://www.flexerasoftware.com/enterprise/company/about/secunia-research/>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:11.listen.asc>
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